Exploring the Extreme Universe with Fermi Gamma-ray Space Telescope (formerly called GLAST)
The third Fermi catalogues of gamma-ray sources and active galactic nuclei · 2015. 10. 28. · The...
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The third Fermi catalogues of gamma-ray sources and
active galactic nuclei
Marcello Giroletti (INAF Osservatorio di Radioastronomia) on behalf of the Fermi-LAT collaboration
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Outline
• Introduction: Fermi and gamma-ray surveys • The third catalogue of gamma-ray sources (3FGL) • The third catalogue of gamma-ray AGNs (3LAC) • Cross-matching high energy and low frequency data (3LAC-
MWACS)
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The Large Area Telescope (LAT) onboard Fermi
• A gamma-ray telescope launched in June 2008 – 20 MeV - 300 GeV photon energies – 2.4 steradian field of view – Aeff:~8000 cm2 at 1 GeV – PSF: θ68%~0.8° at 1 GeV – altitude: 565 km, inclination: 25.6° – 91 min orbital period: views the entire sky
every ~3 hours and provides uniform sensitivity over whole sky in ~day time scale. Great opportunities for
• transients • MWL campaigns on single
sources • all sky survey and population
studies – public data, available within 12 h – operation guaranteed until 2018
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The Third Fermi gamma-ray source catalogue (3FGL, Acero et al. 2015 ApJS)
• 4 years of survey data • Energy range 100 MeV - 300 GeV • 3033 sources
– 2192 at |b|>10° – 1100 un-associated – 25 spatially extended 4
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Evolution of Fermi catalogues
• Catalogues improve not only thanks to longer exposure but also to improved analysis method – instrument characterisation, diffuse model, counterpart
catalogues, etc. • Each catalogue is accompanied by an AGN catalogue
– 0LAC, 1LAC, 2LAC, 3LAC (later slides) • Other catalogues have been produced focused on specific
classes or energy ranges – hard sources, pulsars, GRBs
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catalogue integration #sources% of
unassociated sources
reference
0FGL 3 months 205 18% Abdo et al. (2009)
1FGL 11 months 1451 43% Abdo et al. (2010)
2FGL 2 years 1873 31% Nolan et al. (2012)
3FGL 4 years 3033 33% Acero et al. (2015)
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a quick blazar introduction
• Blazars=flat spectrum radio quasars (FSRQ)+BL Lac type objects (BLL)
• beamed counterparts of radio galaxies, dominated by emission from relativistic jets powered by accretion on SMBH – FSRQ: strong lines in optical
spectra, prominent accretion disk signature, high radio and bolometric luminosity (FR2 counterparts), “red” SEDs
– BLL: weak or no lines, radiatively inefficient accretion disk, low luminosity (FR1 counterparts), “blue” SEDs
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blazar spectral energy distribution (SED)
Low, Intermediate, High synchrotron peaked blazars
LSP ISP HSP
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The Third LAT AGN catalogue (3LAC, Ackermann et al. 2015, ApJ 810, 14)
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• 48 month data set • 2192 TS>25, |b|>10° sources • 3LAC: 1591 counterparts 1563 sources • 1444 AGNs in Clean Sample (no dup., no flags)
• Census : • 415 FSRQs • 602 BLLacs (~50% with measured z) 162 LSPs, 178 ISPs, 272 HSPs, 20 no class. • 413 of unknown type (BCUs) • 23 other AGNs
• Differences between Northern and Southern Hemispheres: 40% of BL Lacs in Southern Hemisphere
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Redshifts
• slightly higher z for new FSRQs relative to 2LAC ones – <z>=1.33 vs. 1.17 – maximum redshift still z=3.1
• 295/604 BL Lacs have no measured redshifts (55%, 61%, 40%) for (LSPs, ISPs and HSPs) – 134 constraints from Shaw et
al. (2013) – Redshift limits for BL Lacs not
compatible with measured redshifts • measured redshifts are
biased low • Are many BL Lacs FSRQs
with emission lines swamped by the non-thermal continuum? 9
2LAC new
2LAC new
HSPs
ISPs
LSPs
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Photon index and spectral curvature
• Little overlap between FSRQ and BLL • New FSRQ slightly softer than 2LAC ones:
<Γ>=2.53 vs. 2.41 • BCU spectral index distribution straddling the
two classes • significant spectral curvature in 91 FSRQ and
32 BLL
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FSRQs
LSP-BLLacs
ISP-BLLacs
νFν
HSP-BLLacs
LAT range
ν
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Spectral photon index vs νpeak
• Correlation between spectral hardness and νpeak confirmed • Lowest index~1.5, as predicted by shock-acceleration models • Same correlation applies to BCUs
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FSRQs LSP-BL Lacs ISP-BL Lacs HSP-BL Lacs
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Radio/gamma-ray connection
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• Pearson coefficient: 0.52 – was 0.47 for 1LAC – which implied a chance
correlation p<1e-7 – also for FSRQ and
BLLacs separately
Ackermann et al. (2011) Pavlidou et al. (2012)
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Improving association methods
• In 3FGL, still a ~1/3 unassociated fraction (>1000 sources!)
• Association of high energy sources to low energy counterparts is generally based on chance of random spatial coincidence – works well for medium-bright gamma-ray sources – low gamma-ray fluxes ~ low radio flux densities ~ high
space density – low gamma-ray fluxes ~ large positional uncertainties
• so: way too many candidates if we only consider spatial coincidence
• Need to add some physics, e.g. VLBI detection, low frequency spectral index, IR colors – e.g. Massaro et al. (2013), Nori et al. (2014), Schinzel et
al. (2013), Lico et al. (in prep.)13
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3FGL-MWACS cross-correlation
• Waiting for SKA and other pathfinder/precursor surveys – MWA commissioning survey (MWACS, Hurley-Walker et al. 2015) – simultaneous 120, 150, 180 MHz data – 6100 sq deg – 120 mJy limiting sensitivity, 3’ angular resolution – 14110 sources… how many (gamma-ray) blazars?
• 186 from BZCat (over 517 sources in same sky area) • 88 from 3LAC (over 249) • given relatively large flux density threshold, mostly are
FSRQs
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BZCat 3LACTotal 186/517 36% 88/247 35%FSRQ 147/327 45% 52/71 73%BLLacs 23/153 15% 19/87 22%BCU 16/37 43% 8/16 50%candidates — — 8/73 11%
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Spectral properties
• From the BZCat, MWACS detects preferably the brightest blazars
• however, there are several undetected BZCat sources that have S1 GHz larger than the MWACS threshold (dotted line) – these must be inverted-spectrum
sources!15
• entire MWACS • <αlow>= 0.81 ± 0.01
• blazars • <αlow>= 0.51 ± 0.05
• gamma-ray blazars • <αlow>= 0.47 ± 0.09
1 GHz flux density distribution all BZcat BZcat w/MWACS det BZcat wo/MWACS det
αlow distribution all MWACS MWACS blazars
preliminarypreliminary
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MWACS-Fermi connection
• no significant correlation between SMWACS and 3FGL energy flux – 82 sources – r=0.27 – p=0.06
• search for UGS counterparts – 13 MWACS matches are
found within r95 of all 3FGL un-associated sources
– but on average 15 are found starting from a fake gamma-ray sky!
• there is potential, but better surveys are needed! – fortunately, they’re on their way!
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preliminary
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Conclusions
• For blazars (and not only), gamma rays are the energy band in which most power is radiated
• Fermi has taken gamma-ray source counts at least even with radio surveys from the ‘70s!
• Great prospects for synergies between radio and gamma-ray surveys for study of the non-thermal universe
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EXTRA SLIDES
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Blazar luminosity functions
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Ajello+ 12
Ajello+ 14
FSRQs BL Lacs
• Rise in HSP-BL Lac density corresponds to a drop-off in FSRQ density
• Evolution of FSRQS into HSPs due to starvation of accreting matter?
Ajello+ 14